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Suspension Tuning & Optimization: Balance, Stability, Control and Grip

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Balance, Stability, Control and Grip

05.27

00:00 - While this isn't a vehicle dynamics course, we can rarely talk about motorsport suspension without having an understanding of some of the basic concepts behind it.
00:08 Put simply, vehicle dynamics is a study of how a car responds to inputs from the driver, the road surface, and aerodynamics as it negotiates a given path.
00:18 When discussing suspension, we can use vehicle dynamics metrics to judge and measure the performance and behaviour of the vehicle.
00:25 These can either be subjective or objective.
00:28 In this module, we'll introduce these metrics so we can make use of them throughout the course as we progress.
00:34 There are a number of different and more in depth definitions for each of the terms in this module but I've tried to stick to simple, useful and practical explanations only.
00:43 Let's start with something we probably all have a fairly good understanding of, grip.
00:48 This simply refers to the forces our tyres can produce.
00:52 The grip we generate between the tyres and the road surface, is the primary metric we're interested in maximising when it comes to optimising our suspension performance.
01:02 Balance is also a commonly used term when discussing vehicle handling.
01:06 When balance is talked about in this context, it's referring to whether a car is oversteering or understeering.
01:13 In simple terms, a car that's understeering through a corner, will follow a wider path than is intended by the driver.
01:19 This is often referred to as push because it can feel like the car is pushing itself towards the outside of the turn.
01:26 Oversteer on the other hand is what we have when the car over rotates and takes a tighter path than the driver intends.
01:33 This is often referred to as the car being loose as it can feel like the rear of the car is loose.
01:38 When in a turn, a car will understeer if the front tyres are the limiting factor and it'll oversteer if the rear tyres are the limiting factor.
01:46 This means that we must have sufficient grip at each end.
01:49 Having a large amount of grip at one end is useless unless we can get sufficient grip at the other end to maintain balance.
01:56 It's also important to understand that understeer is fundamentally a stable condition.
02:01 Which makes it a safer handling trait relative to oversteer.
02:05 Which is fundamentally unstable.
02:07 We can think of it like this, when understeer occurs, if the driver doesn't react, the car will continue on a similar path.
02:14 If the driver doesn't react when oversteer occurs on the other hand, the car will most likely spin.
02:20 Oversteer requires fast and accurate inputs from the driver, typically in the form of opposite lock steering and throttle input to maintain control of the car.
02:28 Road car manufacturers will typically set up their suspension such that the limiting factor is understeer which keeps the limit handling predictable and safe for the average driver.
02:39 In motorsport, this bias is more down towards driver preference and event type.
02:44 In a circuit racing environment, we typically target a small amount of limit understeer.
02:49 Though this can change for different session types, A race versus a qualifying session for example.
02:55 Stability is another fairly self explanatory term that we'll see often.
02:59 But let's look a little deeper into what it actually means within the context of motorsport suspension.
03:06 At its most basic, stability describes the tendency of the car to remain on the current trajectory when subjected to a disturbance.
03:14 An unstable car will need a lot of driver input to keep it on the intended path.
03:19 A lack of stability is seldom good but one area where we're going to see a really big impact on lap time is at corner entry.
03:26 A car that's unstable in the braking zone and corner entry will limit the speed and brake aggression that can be used by the driver.
03:33 Some drivers are more tolerant to low stability than others.
03:36 And in some cases, it can actually be a good thing to reduce the stability of a car as it'll tend to help an understeering car rotate.
03:43 But again this is driver and session type dependent.
03:47 For example we're more likely to target a lower stability setup for qualifying where we want ultimate lap times however for a race, our lack of stability will be harder to manage over a full race and will also be harder on the tyres.
04:00 A lack of stability can be caused by many things but the most common culprits are erratic or unsteady driver inputs, a mismatch in grip between the tyres, incorrect brake bias, poor suspension kinematics, incorrect suspension stiffness balance, bumps in the road or an unsuitable downforce distribution.
04:20 The last useful metric we need to look at is control.
04:23 This describes the amount of authority the driver has over the vehicle to change the direction or path.
04:29 A vehicle with a lot of control will have crisp and direct response to steering inputs whereas a car with a lack of control will tend to be sloppy to respond.
04:39 Having higher level of control may be appropriate in competitions where many quick direction changes take place.
04:44 Or we need to be able to dart between traffic as we make our way around a lap.
04:49 It's not so much that we ever target a setup with less control, it's more that we'll end up reducing some control authority through making a setup change to improve another aspect of our handling.
05:01 Like increasing stability for example.
05:03 In summary, the metrics of grip, balance, stability and control give us a language and a template for describing and characterising the response of the vehicle we're tuning.